1. Technical Field
The present invention relates in general to the digital delivery systems. More specifically, the present invention relates to the delivery of multiformat digital video and digital audio data.
2. Background Art
Digital television offers viewers high-quality audio and video. For broadcasters, the compression of data provided by digital systems allow several programs to be delivered over the same analog bandwidth. Digital television can be distributed using adapted versions of current analog systems, including satellite, terrestrial, and cable. In all these systems, the audio and video components of a program are compressed at the source and multiplexed with other programs and system information needed to recreate the original program. The multiplexed signal is modulated and transmitted to the subscriber""s home. A receiver at the subscriber""s home demodulates the signal to recover the multiplexed digital streams, extracts the program of interest, and decodes the compressed audio and video for presentation on the television.
There are several variations of this system. For example, the digital stream can be modulated and broadcast over a coaxial cable system currently installed or delivered over satellite systems. In addition, the receiver may be a stand alone xe2x80x9cset-top boxxe2x80x9d or may be integrated into directly into the television or other entertainment devices.
There are a variety of possible methods of encoding and delivering the digital television programs. To promote the development of interoperable components from different manufacturers, the Moving Picture Experts Group (xe2x80x9cMPEGxe2x80x9d) has created several different international standards. Of these, the MPEG-2 standard is particularly applicable to the delivery of digital television programs. This standard specifies the format of data as it is broadcast. The standard is composed of three primary parts covering systems, video and audio. The video and audio parts specify the format of the compressed video and audio data, while the systems part specifies the formats for multiplexing the audio and video data for one or more programs as well as information necessary for recovery of the programs. The MPEG-2 standard specifies two stream formats, one for error-free environments such as a digital storage mediums, and one for error-prone environments such as satellite, cable, ATM and other networks. The latter format, often referred to as the xe2x80x9ctransport streamxe2x80x9d is used for broadcast applications. Turning to FIG. 4, a simplified block diagram of a MPEG-2 receiver is illustrated. A tuner extracts the analog signal, which is then digitized. The demodulator recovers the symbols, which represent the incoming bit stream. This group of functions is often referred to as the network interface-module (NIM). The final output of the NIM is the MPEG-2 transport stream, which is then fed into the transport demultiplexor.
The transport demultiplexor extracts the audio and video portions of the program to be sent to the audio and video decoders. The data which specifies the stream content is delivered to memory to enable the processor to configure the receiver to deliver a particular program.
One potential downside to these systems is the inability of these systems to deal with other types of data. For example, previous MPEG-2 receivers have been limited by their inability to deal with other types of video and audio data. Specifically, the real time constraints on MPEG systems requires dedicated hardware that cannot be easily adapted to receive other types of data formats.
Specifically, in current receivers, real-time constraints on synchronization and clock recovery require that the initial stages of the transport demultiplexor be implemented in hardware. These transport demultiplexors require that the data be in the correct MPEG-2 transport syntax. Otherwise, the data cannot be processed correctly.
Thus, what is needed is an improved receiver with that can receive and process other data information in addition to maintaining real-time processing support for MPEG-2 transport streams.
The preferred embodiment of the present invention provides an improved receiver that can receive and process many different data types in addition to decoding MPEG-2 transport streams. For example, the preferred embodiment can be used to process data Asynchronous Transfer Mode (ATM), Digital Versatile Disc (DVD), and other transport streaming formats. The preferred embodiment minimizes hardware complexity by using the same loaders for both MPEG-2 and alternative stream data. The preferred embodiment utilizes a bypassable synchronizer and a bypassable packet parser to allow alternative data streams to be sent to system memory for decoding by a the host processor. When receiving MPEG-2 transport streams, the bypassable synchronizer and bypassable packet parser are used to synchronize and filter the MPEG-2 transport stream. The parsed MPEG-2 streams are then loaded into a packet buffer and passed to the video and audio decoders. When non-MPEG-2 stream data is provided, the bypassable synchronizer and bypassable packet parser instead forward the data to the packet buffer without performing synchronization or filtering. There, the non-MPEG-2 stream data is loaded into system memory. In memory, the non-MPEG-2 data can be decoded by the CPU and then passed onto the video and audio decoders. Thus, by selectively bypassing synchronizer and packet parser, the preferred embodiment allows the receiver to decode non-MPEG-2 data streams while maintaining the ability to perform real time decoding of MPEG-2 streams. Additionally, the preferred embodiment facilitates this dual purpose while minimizing device complexity.